The present invention relates to variations of techniques described in U.S. Pat. No. 5,611,726. Reference is also made to Ser. No. 08/889,768 filed Jul. 8, 1997 and to Ser. No. 08/466,451 filed Jun. 6, 1995, and its parent applications Ser. No. 08/391,250 filed Feb. 21, 1995, Ser. No. 08/055,856 filed Apr. 10, 1993, now U.S. Pat. No. 5,390,431 as well as U.S. Pat. No. 5,404,679. All of the details of these patents and applications are incorporated herein by reference thereto.
U.S. Pat. No. 5,611,726 ('726 patent) describes unique blade sharpeners that incorporate novel honing materials to create highly sharp yet durable knife edges. That patent described the importance of obtaining optimum physical properties of the honing material. It must have sufficient flexibility, yet when physically distorted in use it must be able to recover its original physical shape. If the honing disks are too stiff they will damage the knife edge. The grit size must be selected to be sufficiently aggressive but not so aggressive as to injure the edge.
Attempts by the inventors to use known conventional abrasive systems proved unsuccessful in attempts to reproducibly create highly sharp and durable knife edges. Successful honing requires that the material incorporating the abrasives have the appropriate physical properties, flexibility, resilience, stiffness, thermal properties and an adequate but not too high ablating rate with little to no aging of its properties.
Attempts to use conventional buffing means proved unsuccessful. Cloth and fibrous wheels tested by the inventors proved to be nonuniform and had to be recoated frequently with abrasives in order to retain their effectiveness. They are unpredictable and inconsistent. Wheels of leather and porous polyurethane materials (such as Corfam.RTM.) were impractical as they "load up" with sharpening debris and were unpredictable and inconsistent in performance.
The inventors reported in the '726 patent details of their search for materials that can be formed into precise shapes that will if distorted recover to their original shape and be homogeneous in properties. Angular control, important in knife sharpening, relies on precise shapes for the abrasive and honing materials that contact the knife edge. It was shown that a satisfactory material falls within a narrow range of physical properties for their performance.
Rubbers and polyurethanes that incorporate abrasives proved to be impractical in that they loaded-up too rapidly or that they were too tough to ablate adequately. A wide variety of epoxy-like materials proved unsatisfactory because of excessive brittleness, excessive "loading-up" and glazing over of their surfaces. They also tended to change properties with age, softened when heated or were not sufficiently flexible. However, as disclosed in the '726 patent the inventors found an optimum epoxy composition composed largely of polyoxypropylene amines which are aliphatic poly ether primary and di-and tri-functional amines derived from propylene oxide abducts of diols and triols. This material has the necessary flexibility, durability and recovery properties to make a good honing material. It has the necessary conformity as molded while maintaining the necessary abrasiveness when loaded, it has toughness, durability and adequate rubber-like properties to maintain its shape over long periods of use.
While this optimum material performs well, it must be formed into final shape by a long, tedious and expensive casting process that sets the final properties in 1-2 hours at 212.degree. F. but requires added curing of 4 hours at 220-230.degree. F. to stabilize its properties for a period of years.
Conventional methods of characterizing this finished epoxy material proved impractical. It was found however, that a modified Wilson Rockwell tester equipped with a special 7/8" diameter smooth steel ball did give very reproducible measurements that correlated with those properties of this material essential to its intended use for knife sharpening.
This method is described below:
The test method uses a standard Wilson Rockwell tester equipped with a 7/8" diameter steel ball to compress under the ball a sample of this material 2.times.2 inches and 3/8" thick first with a standard minor weight of 10 Kilograms and then with a major weight of 60 Kilograms. The ball is lowered onto the sample first under the load of the minor weight and an initial rest height of the ball is indicated as the zero point. The major weight is then applied to the ball and the distance that the ball penetrates below the zero point (change in height) is noted as D.sub.1. The major weight is removed while the minor weight remains and the remaining amount of penetration is reduced. The remaining amount of depression below its original zero point is recorded as D.sub.2. With this procedure a sample of the optimum epoxy material of this invention in less than 30 seconds compressed 229 divisions (0.0183 inches) on the Rockwell Hardness Tester when the major weight was applied. This is D.sub.1. When that major load was removed the remaining depression D.sub.2 was 140 divisions (0.0112 inches). The recovery, R, equal ##EQU1## With all weights removed this material returned to more than 98% of its original thickness within 30 minutes. Compositions with lighter abrasive loading of the unique epoxy material recovered faster to the original thickness after this test. The recovery R as defined above and the subsequent recovery of the disks to their original shape are critically important properties for the optimum performance of these disks.
Samples representative of satisfactory compositions for the epoxy abrasive loaded disks were tested as shown below:
______________________________________ % Abrasive D.sub.2 Remaining* Solids in R Depression (with 10 Kg) Sample # Epoxy 37-3EC % Recovery Divisions ______________________________________ 1 78% 31 155 2 74% 39 140 3 50% 75 ______________________________________ *1 Division equals 0.00008 inches of Depression.
As reported in the '726 patent, this represents a relatively narrow range of properties that gives satisfactory performance using 5 micron grit. The optimum composition is in an even narrower range of 65-75% using the 5 micron grit. This demonstrates the criticality of the composition and the resulting physical properties.
The typical values stated above produced satisfactory sharpness and cutting characteristics desired by the professional chef.
Satisfactory cutting edges were produced with honing disks made by adding abrasive particles of a size within the range 1-20 microns approximately 40% to 80% by weight in the epoxy mixture. Within these ranges it is preferable to use smaller particles in the upper portion of the range of abrasive loading.
While the epoxy based composition provided the unique properties needed for good honing as described in the '726 patent, the epoxy material must be produced as described only by a slow casting process.